Data input devices or finger navigation devices, such as computer mice, touch screens, trackballs, scroll wheels and the like, are well known for inputting data into and interfacing with personal computers or workstations. Such devices allow rapid relocation of a cursor on a monitor, and are useful in many text, database and graphical programs. A user controls the cursor, for example, by moving the mouse over a surface to move the cursor in a direction and over distance proportional to the movement of the mouse.
Computer mice, for example, come in both optical and mechanical versions. Mechanical mice typically use a rotating ball to detect motion, and a pair of shaft encoders in contact with the ball to produce a digital signal used by the computer to move the cursor. One problem with mechanical mice is that they are prone to inaccuracy and malfunction after sustained use due to dirt accumulation, etc. In particular, mechanical mice have not demonstrated the accuracy demanded in state-of-the-art mice today, which generally must have a path error of less than 0.5%. In addition, the movement and resultant wear of the mechanical elements, particularly the shaft encoders, necessarily limit the useful life of the device.
One solution to the above problems with mechanical mice has been the development of mice using an optical navigation system. These optical mice have become very popular because they provide a better pointing accuracy and are less susceptible to malfunction due to accumulation of dirt.
The dominant technology used today for optical mice relies on a light emitting diode (LED) illuminating a surface at or near grazing incidence, a two-dimensional CMOS (complimentary metal-oxide-semiconductor) detector which captures the resultant images, and software that correlates successive images to determine the direction, distance and speed the mouse has been moved. This technology provides high accuracy but suffers from a complex design and relatively high image processing requirements.
Another approach uses one-dimensional arrays of photo-sensors or detectors, such as photodiodes (PDs), and a coherent light source, such as a laser. Light from the coherent source scattered off of an optically rough surface generates a random intensity distribution of light known as speckle. Successive images of the surface are captured by imaging optics, translated onto the photodiodes, and compared to detect movement of the mouse. The photodiodes may be directly wired in groups to facilitate motion detection. This reduces the photodiode requirements, and enables rapid analog processing. The use of a speckle-based pattern has several advantages, including efficient laser-based light generation and high contrast images even under illumination at normal incidence. This allows for a more efficient system and conserves current consumption, which is very important in wireless applications.
Although a significant improvement over prior LED/CMOS-based optical mice, these speckle-based devices have not been wholly satisfactory for a number of reasons. In particular, conventional optical mice include one or more openings in an enclosure enclosing the device through which light is emitted and transmitted to the photo-sensors or detectors. By opening it is meant there is substantially no barrier or screen between illumination and imaging optics or lens, or between the light source and photo-sensors. Thus, these openings render the optical navigation system susceptible to the penetration of dust and other foreign objects, which interfere with operation of the device.
Another type of finger navigation device is a touch pad which detects movement of a stylus or finger over a surface of the pad. Generally, conventional touch pads rely on small changes in capacitance or resistance to sense movement across the pad surface. One problem with this approach is that the touch pads are prone to inaccuracy and malfunction after sustained use due to dirt accumulation and deforming of the pad surface. Thus, it would be desirable to have an optical or light-based touch pad. However, this has not been possible heretofore due to interference from ambient light in the environment.
Accordingly, there is a need for an optical navigation system that has a low path error, and is less susceptible to the penetration of dust and other foreign objects. It is further desirable that the optical navigation system is substantially invulnerable to interference from ambient light in the environment.
The present invention provides a solution to these and other problems, and offers further advantages over conventional optical navigation systems.